Re: [TLS] Possible TLS 1.3 erratum

Hubert Kario <hkario@redhat.com> Tue, 20 July 2021 10:39 UTC

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From: Hubert Kario <hkario@redhat.com>
To: Peter Gutmann <pgut001@cs.auckland.ac.nz>
Cc: Ilari Liusvaara <ilariliusvaara@welho.com>, <tls@ietf.org>
Date: Tue, 20 Jul 2021 12:38:48 +0200
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Subject: Re: [TLS] Possible TLS 1.3 erratum
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On Monday, 19 July 2021 21:37:08 CEST, Peter Gutmann wrote:
> Hubert Kario <hkario@redhat.com> writes:
>
>> It only doesn't matter if you don't want to verify the certificate...
>> 
>> It's one thing to be able to be able to verify an RSA-PSS signature on TLS
>> level, it's entirely another to be able to properly handle all 
>> the different
>> RSA-PSS limitations when using it in SPKI in X.509.
>
> Is there anything that's jumped through all the hoops to 
> implement the complex
> mess that is PSS but then not added the few lines of code you need do verify
> it in certificates?  And if so, why?

I suggest you go back to the RFCs and check exactly what is needed for 
proper
handling of RSA-PSS Subject Public Key type in X.509. Specifically when the
"parameters" field is present.

You definitely won't be able to implement it in just "few lines".

> In any case it's still encoding a minor implementation artefact of the
> certificate library being used into the TLS protocol, where it 
> has absolutely
> no place.  You either do PSS or you don't, and the TLS layer doesn't need to
> know what magic number you use to identify it in certificates.

1. It's not minor
2. "What certificates can peer accept" is totally within the purview of 
TLS.
   It's like that for Raw keys, it's like that for GPG certificates, it's
   like that for RSA vs ECDSA vs DSA certificates, and now it's also for
   RSA-PSS.
-- 
Regards,
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purky┼łova 99/71, 612 45, Brno, Czech Republic